1. Field of the Invention
The present invention relates to a new aromatic polyester and aromatic polyester amide which has outstanding heat resistance, chemical resistance, dimensional stability, flame retardance, and mechanical strength, and is capable of injection molding, extrusion molding, blow molding, and spinning at a temperature lower than 340.degree. C.
The present invention also relates to filaments of said aromatic polyester and aromatic polyester amide, said filaments having outstanding heat resistance, chemical resistance, dimensional stability, flame retardance, and mechanical strength.
The present invention further relates to compositions of said aromatic polyester and aromatic polyester amide, each containing an inorganic filler or magnetic powder, said compositions having outstanding heat resistance, chemical resistance, dimensional stability, flame retardance, and mechanical strength.
2. Description of the Prior Art
It is known that it is possible to produce a polyester which exhibits the melt anisotropy. A polymer of this kind is generally called thermotropic liquid crystalline polymer. It is also known that this liquid crystalline polymer provides, when spun or molded in its molten state, fibers or molded articles having high strength, high modulus, and high heat resistance. Of the liquid crystalline polymers, aromatic polyester are generally known, and homopolymers and copolymers of p-hydroxybenzoic acid are commercially available.
A disadvantage of these aromatic polyesters is that they have such a high melting point that they are incapable of spinning and melt molding and they have such a high melt viscosity that they need high temperatures for spinning and molding.
To overcome this disadvantage, investigations are being made to lower the melting point by copolymerizing p-hydroxybenzoic acid with another component. A copolymer component used for this purpose is one which has a flexible aliphatic chain or a flexing structure.
An example of the liquid crystalline polyester copolymerized with an aliphatic chain is disclosed in Japanese Patent Laid-open No. 84821/1983. This polyester is composed of p-hydroxybenzoic acid, polyethylene terephthalate, aromatic diol, and aromatic dicarboxylic acid. It has a melting point as low as 280.degree.-300.degree. C. and is superior in spinnability and moldability. It provides filaments having a high strength of 7-11 g/d after heat treatment.
The filaments of the polyester have a disadvantage that they have a tensile modulus as low as 400 g/d (.apprxeq.50.6 GPa) and are liable to form gel resulting from the thermal decomposition of aliphatic chains that takes place in the stage of spinning or synthesis, because the polymer contains aliphatic chains in the molecule. This gel causes filament breakage in the stage of spinning and poor appearance and lower strength of filaments obtained.
Another disadvantage of the aliphatic-containing liquid crystalline polymer is that it is by far lower in wet-heat stability than wholly aromatic liquid crystalline polyesters and that the molded article and fiber thereof greatly decrease in strength when placed in a hot, humid atmosphere.
On the other hand, an example of the polyester copolymerized with a flexible component is a wholly aromatic polyester containing 2,6-naphthalene diol, which is disclosed in Japanese Patent Laid-open No. 50594/1979 and U.S. Pat. No. 4,188,476. It is composed of p-hydroxybenzoic acid, terephthalic acid, and 2,6-naphthalene diol (according to said Japanese Patent), or it is composed of p-hydroxybenzoic acid, terephthalic acid, 2,6-naphthalene diol, and m-hydroxybenzoic acid (according to said U.S. Patent). It has a comparatively low melting point of 320.degree.-350.degree. C. owing to the flexible structure of 2,6-naphthalene diol. In addition, it has good moldability and provides filaments having a high strength of 15 g/d after heat treatment. Being a wholly aromatic polyester, it is not liable to form gel resulting from thermal decomposition and it is free of problems associated with filament breakage, poor appearance and strength decrease.
However, this polyester still has a disadvantage that it only provides filaments having a low tensile modulus of 500-600 g/d (.apprxeq.63.3-76.0 GPa) even after heat treatment. Therefore, it is not suitable for use in the area, such as fiber reinforced plastics, where high moduli are necessary.
Another example of the liquid crystalline polyester containing 6-hydroxy-2-naphthoic acid as the flexible component is disclosed in Japanese Patent Laid-open No. 62630/1984. It is composed of p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, 4,4'-dihydroxybiphenyl, and terephthalic acid. It provides filaments having a high tensile strength (about 23 g/d) and a high tensile modulus (about 1000 g/d=126.6 GPa). Being a wholly aromatic polyester, it is free of the gelation problem.
The above-mentioned wholly aromatic liquid crystalline polyesters involve several problems to be solved. That is, they need a molding temperature as high as 345.degree.-370.degree. C., which causes the thermal decomposition of resin in the spinning apparatus and molding machine, therefore a special molding or spinning apparatus which have the ability of molding or spinning continuouslly at high temperature is needed.
An example of the liquid crystalline polyester containing 2,6-naphthalene dicarboxylic acid is disclosed in Japanese Patent Laid-open No. 284221/1988 (U.S. Pat. No. 4,851,497). The liquid crystalline polyester has a disadvantage that it provides filament having a low modulus of 72 GPa even after heat treatment. Therefore, it can not provide improved high regid filament
For reasons mentioned above, there has been a demand for a new liquid crystalline polyester having a high tensile modulus, high tensile strength, good moldability, good spinnability, and good wet-heat stability.
In the meantime, liquid crystalline polyester amide has been developed by introducing an amide linkage into a liquid crystalline polyester in order to improve the properties of liquid crystalline polyester, such as adhesion properties, fatigue resistance, and anisotropy (difference in physical properties observed in the direction of resin flow [MD] and the direction perpendicular to the direction of resin flow TD]). Examples of liquid crystalline polyester amide are disclosed in Japanese Patent Laid-open Nos. 137321/1982, 45123/1982, 172921/1982, 177019/1982, 177020/1982, 77021/1982, 29820/1983, 1722/1983, 89618/1983, 5103/1986, 36819/1986, 236826/1986, and 236827/1986.
These liquid crystalline polyester amides do not have the problems associated with anistropy which are common in the above-mentioned aromatic polyesters. Nevertheless, they still have disadvantages resulting from the introduction of amide groups. That is, they are poor in heat resistance and thermal stability (in other words, they decrease in mechanical strength when exposed to an environment at a high temperature for a long time). They are poor in weather resistance (in other words, they decrease in physical properties upon exposure to ultraviolet rays). They have a high melt viscosity (which leads to poor flowability and hence poor moldability). These drawbacks are more significant as the content of the amide component increases. In fact, the above-mentioned characteristic properties are considerably deteriorated when the content of amide linkage is high enough to relax the anisotropism sufficiently. Therefore, liquid crystalline polyester amide is of less practical use than liquid crystalline polyester.
It is known that liquid crystalline polyester and/or liquid crystalline polyester amide is incorporated with an inorganic filler for the improvement of heat resistance, scratch resistance, stiffness, and anisotropy, as disclosed in Japanese Patent Laid-open No. 38464/1989.
The incorporation of an inorganic filler improves the above-mentioned characteristic properties (i.e., heat resistance, scratch resistance, stiffness, and anisotropism). On the other hand, it poses problems associated with the decrease of impact strength and the deterioration of moldability (or flowability). The latter is particularly serious for the conventional wholly aromatic liquid crystalline polyester and/or wholly aromatic liquid crystalline polyester amide which needs a higher molding temperature than other resins. For this reason, there has been a demand for a wholly aromatic liquid crystalline polyester and/or wholly aromatic liquid crystalline polyester amide which contains an inorganic filler and yet exhibits good moldability.
In the meantime, a resin composition containing a magnetic powder is in general use, although inferior in magnetic properties to sintered magnets, owing to its advantage that it provides desired products, light in weight and complex in shape, by simple multi-cavity injection molding.
This resin composition is made with a binder resin such as epoxy resin and polyamide resin (e.g., nylon 6 and nylon 66). The binder resin determines the mechanical strength and heat resistance of the resin composition containing a magnetic powder. If the binder resin is epoxy resin or nylon, the heat distortion temperature of the resin composition will be 100.degree.-120.degree. C. or 140.degree.-160.degree. C., respectively.
The resin composition containing a magnetic powder should have high heat resistance so that it finds more uses. However, high heat resistance has so far been achieved at expense of moldability, and poor moldability offsets the advantage of being capable of complex molding and multicavity molding.